The present invention relates to a two-way valve for a tap of a gas cylinder, said valve being intended to be fitted on a selectively openable gas inlet/outlet passage of said tap, said two-way valve permitting both filling and discharging gas into and from the cylinder, respectively, and comprising a casing having a gas flow passage and at least one lateral opening formed in a casing wall; a piston means disposed in said casing and having a gas flow passage therethrough communicating with said casing passage, resiliently yieldable means for moving the piston means to a closed position wherein the opening is sealed off from said casing passage, and said piston means being movable by the pressure of the filling gas against the action of the resiliently yieldable means to an open position in which the lateral opening is in communication with the casing passage; a level controlling valve movable between open and closed positions and, when in said open position, permitting gas to flow between the gas cylinder and the inlet/outlet passage through said casing and piston passages; means for detecting the filling level in the gas cylinder and for actuating the level controlling valve in response to said level, said level controlling valve, when not held in an open position by said detecting means, being openable by the pressure of the gas in the cylinder when the inlet/outlet passage is open; at least one vent orifice formed through said casing wall; and seal means to block communication through said orifice between the casing passage and the environment surrounding the casing in the gas cylinder when the pressure in the casing passage is below a predetermined value and to establish such communication through said orifice when the pressure in the casing passage is above said predetermined value and while the piston means in the closed position. The invention also relates to a tap provided with such a two-way valve.
A gas tap with such a two-way valve is disclosed in the U.S. Pat. No. 5,487,404 issued on Jan. 30, 1996 to L. Kerger, which is incorporated herein by reference. As described in this prior US patent when the tap is closed after the level controlling valve has been closed by the action of the float, a certain volume of gas remains trapped inside the valve and the inlet pipe of the tap and causes a danger of explosion in the event of overheating. In order to avoid such a danger a vent orifice has been provided in the wall of the valve casing which allows this gas volume to flow into the cylinder after closing of the tap so as to be within the field of action of the tap safety valve. The cross-section of this vent orifice must be small so that a sufficient pressure may build up within a valve chamber between the sealing device and the level controlling valve, after the level controlling valve has been closed, to cause the sealing device to move into a position closing the lateral openings. Despite the small vent orifice, it nevertheless has a negative influence on the speed of closure of the valve piston and therefore, in the above mentioned U.S. Pat. No. 5,487,404 to L. Kerger the orifice is associated with an outer resilient sealing ring disposed about the valve casing on the outer surface thereof, which resists the maximum filling pressure in order to ensure the leak tight closure of the orifice and which yields at a pressure greater than the filling pressure in order to open the orifice to permit discharge of the enclosed gas volume from the valve chamber into the cylinder when the pressure increases beyond a certain threshold value in the valve chamber. The sealing device of the valve disclosed in the above mentioned U.S. Pat. No. 5,487,404 to L. Kerger has two further sealing rings one of which providing leak tight engagement between the valve piston and the surrounding casing wall and the other cooperating with a seating surface of the valve casing and leak tightly engaging the seating surface in the closed position of the valve piston. The three sealing rings increase the complexity of the valve structure and the outer seal ring may be inadvertently damaged or even lost prior to assembly of the valve with a gas cylinder.
In accordance with the invention the seal means blocking and establishing communication between the casing passage and the environment surrounding the casing is on said piston means and movable therewith and is in leak tight slideable engagement with an inner surface of said casing wall, said seal means being effective to block and establish communication between said vent orifice and the casing passage when the pressure in said passage is below and above said predetermined value, respectively, and while the piston means is in the closed position.
Accordingly, the seal means on the piston means providing fluid tight engagement between the piston means and the surrounding casing wall inner surface is at the same time the seal means to block or establish communication between the interior casing chamber and the environment surrounding the valve casing in the gas cylinder, thereby eliminating one seal means and simplifying the overall construction of the two-way valve. In addition, the seal means blocking or establishing communication between the orifice or orifices and the casing passage is now in the interior of the valve casing and accordingly the risk of loss or undesired damage to the seal means is eliminated.
In one particular embodiment the piston means is adapted to be urged in response to the pressure in the casing passage exceeding the predetermined value an additional increment of movement in closing direction to a venting position in which the lateral opening remains sealed off and the vent opening is in communication with the casing passage. In this embodiment the piston means has a further seal means adapted to leak tightly engage a seating surface in the interior of the casing in the closed position of the piston means and the further seal means is of an elastomeric material resisting movement of the piston means to the venting position when the pressure in the casing passage is below the predetermined value and being elastically yieldable to permit movement of the piston means to the venting position when the pressure in the casing passage exceeds the predetermined value. Preferably the seating surface is a tapered seating surface and the further seal means has a tapered sealing surface that is non-parallel to the tapered seating surface. The angle of taper of the sealing surface may be smaller than the angle of taper of the seating surface. In the preferred embodiment the piston means has an annular body member and the first mentioned seal means comprises a flexible annular sealing lip extending from the annular body member of the piston means and diverging radially outwardly to leak tightly engage the casing inner surface as it extends away from the piston means body member. Further, the first mentioned seal means and the further seal means are preferably integral portions of a unitary seal member having the first mentioned seal means and the further seal means located on opposite end faces of the piston means body member and having an annular intermediate section interconnecting the two seal means and snugly matching an inner wall of the piston means body member. The unitary seal member is preferably bonded by vulcanization to the piston means body member.
The first mentioned seal means may be elastically yieldable and collapsible towards the piston means body member when exposed to a pressure in the casing passage exceeding the predetermined value to assist in establishing the communication between the vent orifice and the casing passage.
In another embodiment, the communication between the vent orifice and the casing passage is established solely by the first mentioned seal means yielding or collapsing towards the piston means body member when exposed to a pressure in the casing passage exceeding the predetermined pressure. In this modified embodiment the piston means is not movable to a venting position, but only yielding or collapsing of the first mentioned seal means controls opening and closing of the vent orifice to establish or block the communication between the vent orifice and the casing passage.
It can be seen that in one embodiment three different seal ring means of the prior art valve structure have been replaced by a single unitary seal member which serves to tightly engage the interior cylindrical wall surface of the valve casing, which serves as valve sealing means to tightly engage the valve seat in the closed position, and which serves to cover or uncover the vent orifice in the valve casing.